1. Field of the Invention
The present invention relates to a vibration wave driven apparatus and an image pickup apparatus.
2. Description of the Related Art
Vibration wave driven apparatuses that are applied to products for driving camera lenses or the like include a bar-type vibration wave driven apparatus. Japanese Patent Laid-Open No. 2008-187805 discloses a bar-type vibration wave driven apparatus in which the output of a rotor is transmitted to an external device with a gear interposed therebetween. The mechanism of the known vibration wave driven apparatus will now be described with reference to FIGS. 10A and 10B. FIG. 10A is a cross-sectional view of the known bar-type vibration wave driven apparatus. FIG. 10B is a perspective view of a part where the rotor and the gear engage with each other.
In FIG. 10A, a first elastic body 1, a second elastic body 2, and a multilayer piezoelectric device 3 are fastened by a shaft 4 and a nut 5 with a specific clamping force. A rotor 7 has one surface (the lower end in the drawing) thereof being in contact with a wear-resistant member 6. The wear-resistant member 6 is provided at the upper end of the first elastic body 1. A gear 8 is provided so as to face the other surface of the rotor 7. The gear 8 rotates with the rotor 7 and transmits the output of the vibration wave driven apparatus to an external device. The position of the gear 8 is fixed in a thrust direction along the shaft 4 by a flange (attaching portion) 10 provided for attachment of the vibration wave driven apparatus. A pressure spring 15 for applying a pressure to the rotor 7 is provided between the gear 8 and the rotor 7.
As shown in FIG. 10B, the rotor 7 has a circular recess 7c and in the top surface thereof a pair of grooves 7a and 7b extending radially and axisymmetrically with each other. The gear 8 has on the bottom surface thereof a cylindrical projection 8c configured to engage with the circular recess 7c of the rotor 7, and a pair of projections 8a and 8b (the projection 8b is not shown) configured to engage with the grooves 7a and 7b, respectively, of the rotor 7. With such engagements, the rotation of the rotor 7 is transmitted to the gear 8 and is output.
In the known vibration wave driven apparatus, the gear 8 and a gear of the external device that receives the output from the gear 8 are spur gears. Therefore, the optical axis of a lens barrel of a camera and the axis of rotation of the vibration wave driven apparatus are to be arranged substantially parallel to each other.
On the other hand, the substantially parallel arrangement of the optical axis of the lens barrel and the axis of rotation of the vibration wave driven apparatus restricts the flexibility in the arrangement of the vibration wave driven apparatus. Therefore, further improvement has been demanded for efficient utilization of space.